/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.consensus.iot.snapshot;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;

public class SnapshotFragmentReader {

    private static final int DEFAULT_FILE_FRAGMENT_SIZE = 10 * 1024 * 1024;
    private final String snapshotId;
    private final String filePath;
    private final SeekableByteChannel fileChannel;
    private final long fileSize;
    private final ByteBuffer buf;
    private long totalReadSize;
    private SnapshotFragment cachedSnapshotFragment;

    public SnapshotFragmentReader(String snapshotId, Path path) throws IOException {
        this.snapshotId = snapshotId;
        this.filePath = path.toAbsolutePath().toString();
        this.fileSize = Files.size(path);
        this.fileChannel = Files.newByteChannel(path);
        this.buf = ByteBuffer.allocate(DEFAULT_FILE_FRAGMENT_SIZE);
    }

    public boolean hasNext() throws IOException {
        buf.clear();
        int actualReadSize = fileChannel.read(buf);
        buf.flip();
        if (actualReadSize > 0) {
            cachedSnapshotFragment =
                    new SnapshotFragment(snapshotId, filePath, fileSize, totalReadSize, actualReadSize, buf);
            totalReadSize += actualReadSize;
            return true;
        }
        return false;
    }

    public SnapshotFragment next() {
        return cachedSnapshotFragment;
    }

    public void close() throws IOException {
        if (fileChannel != null) {
            fileChannel.close();
        }
    }
}
